1. Field of the Invention
The present invention relates to a synchronization system and method used for a mobile communication system. More particularly, the present invention relates to a system and method for synchronizing broadcast/multicast service frames provided in a mobile communication system.
2. Description of the Related Art
Mobile communication systems were originally designed to provide a voice communication service allowing user mobility. Along with rapid development of the technology, the mobile communication system now provides various services in various fields to meet user demand. The latest mobile communication system can provide not only an SMS service but also email, Internet and broadcast services. To provide the various services, a synchronous Code Division Multiple Access (CDMA) system has evolved to an IS-95 system and then to a CDMA-2000 system, which has been commercialized in some areas. A high-speed data only system, called First Evolution-Data Only (1xEV-DO), was then introduced, and a system enabling high-speed data transmission and voice communication at the same time, which is called First Evolution-Data and Voice (1xEV-DV), was then introduced. Many parts of the 1xEV-DV system are under discussion in the standardization bodies.
Since the CDMA system basically uses a synchronous mode, it operates within a synchronized network. However, with network synchronization, it is difficult for the mobile communication system to provide broadcast services. This is due to the fact that it has been proposed that the mobile communication system provide broadcast services by interworking with a contents server connected to the system, instead of providing broadcast services using radio waves. Some example systems capable of providing broadcast services are CDMA 2000, CDMA 1xEV-DO, and CDMA 1xEV-DV systems. A conventional network structure and operation for providing broadcast services, for example, using the CDMA 1xEV-DO system will now be described with reference to FIG. 1.
FIG. 1 is an illustrative diagram of the configuration of a CDMA 1xEV-DO system implemented for providing broadcast services. The CDMA 1xEV-DO system includes an Access Terminal (also referred to as a “mobile terminal” or a “mobile station”) (AT) 100, and first and second Access Networks (ANs) 110 and 120, Packet Control Functions (PCFs) 130a and 130b, a Packet Data Service Node (PDSN) 140, and an authentication system 150 which are implemented to provide high-speed data services to the access terminal 100. The CDMA 1xEV-DO system further includes a Broadcast/Multicast Service (BCMCS) controller 160 and a BCMCS content server 170 for providing broadcast services. The configuration of the 1x EV-DO mobile communication system for providing high-speed data services to the access terminal will now be described in detail with reference to FIG. 1.
The access network 110 has a specific wireless communication area, and includes Access Network Transceiver Systems (ANTS) 111a to 111n for providing data services to the access terminal 100 through radio channels established with the access terminal 100, and an Access Network Controller 112 for controlling the ANTSs 111a to 111n. The access network 120 has a specific wireless communication area, and includes Access Network Transceiver Systems (ANTS) 121a to 121n for providing data services to the access terminal 100 through radio channels established with the access terminal 100, and an Access Network Controller 122 for controlling the ANTSs 121a to 121n. The following description will be given based on the access networks 110 and 120 except when their ANTSs and ANCs must be distinguished from each other.
The PCFs 130a and 130b are connected respectively to the access networks 110 and 120 to control processing for providing broadcast services and high-speed data services to the access networks 110 and 120. The PCFs 130a and 130b are also connected to the PDSN 140, which is a termination node for connection to the Internet or other networks to provide data services in the mobile communication system. The PDSN 140 is connected to the authentication system 150 for authentication of terminals in the mobile communication system.
The authentication system 150 includes an Access Network Authentication, Accounting and Authorization (AN-AAA) system 151 for authentication of the 1x EV-DO system, and an AAA system 152 for authentication of other networks such as Internet and broadcast service networks.
The BCMCS content server 170 is a server for providing broadcast/multicast services to the PDSN 140. The BCMCS content server 170 produces broadcast data, including video and audio data for broadcasting, into Internet Protocol (IP) packets, and provides the broadcast data IP packets to the PDSN 140. The BCMCS controller 160 controls the BCMCS content server 170, and determines whether the broadcast service is to be provided to the terminal, according to the user authentication result.
The CDMA 1xEV-DO system can provide the broadcast service based on the above configuration as shown in FIG. 1. Higher nodes of the access networks 110 and 120 provide the broadcast service to the access networks 110 and 120 in an IP multicast scheme. However, the access terminal 100 may be in motion while receiving the broadcast service. The packet data service is also liable to cause a time delay. To provide the broadcast service to the access terminal 100 properly regardless of whether the access terminal 100 is in motion, BCMCS traffic must be transmitted from the access networks simultaneously to the access terminal 100. However, packets for providing the broadcast service may be transmitted to the access networks with different time delays. The time delays depend on characteristics of the packets and the amount of BCMCS traffic.
Since the BCMCS traffic is transmitted using the packets, the access networks may provide packets or frames of the same broadcast service at different times. This problem is critical when performing handoff of the broadcast service. It is also practically impossible for the access terminals to combine and use traffic frames received simultaneously from a number of access networks (also referred to as “base stations”). Further, the access terminal may recognize traffic of the same broadcast service, provided from another base station near the access terminal, as noise.